Organic light-emitting diodes made with poly (N-vinylcarbazole) (PVK) and 8-hydroxyquinoline aluminium (Alq3)

Organic light-emitting diodes made with poly(N-vinylcarbazole) (PVK) and 8-hydroxyquinoline aluminium (Alq3) were fabricated. PVK served as hole-transport layer, and Alq3 played a role of emitting layer. The effect of the thickness of the Alq3 layer on the brightness and the luminous efficiency of the devices was investigated. When the thickness was around 70 nm, the brightness reached the maximum value, 2300 cd/m2. But the efficiency increased with the film thickness of the Alq3 layer in the range from 26 to 165 nm. The optimum film-forming concentration of the PVK layer was also studied by inspecting the quality of the film by scanning electron microscopy. It was found that the film quality of PVK layer was the best when the concentration of PVK solution was 4.0 mg/ml, and the specification of the device fabricated under this condition was also best.